Where you just can’t stop tinkering.
The machine started somewhat and I did a quick check to see that the HALT line and RESET line were both ok, indicating that the CPU is in working mode.
I was googleing on various 68000 related diagnostics issues when a single post caught my eye that talked about odd and even roms. An Eureka moment ensued.
I always figured, since I dumped both EPROM’s, that they were corrupt. Nearly empty and unable to decompile into anytyhing usefull. But if the 68K uses odd & even byte addressing on different parts of its databus, all of a sudden, the world makes sense. They both contain the boot code, eprom 1 EVEN and eprom 2 ODD. A small pythonscript to combine the two into a single bin file, deassemble it and compared it to the boot source code I have and it seems on point. So:
- The roms are NOT corrupt
- I need to split my diagnostic roms in EVEN and ODD roms.
When I turn on the machine on the original ROM’s, there’s a very faint low buzzing coming from the speaker (and mind you, this is the orignal speaker so after it’s humid ordeal and being ripped of the front plate, its forgiven for not making that much of a fuzz anymore….
So I turned my attention to the source code:
And indeed:
bados: ; Sound low buzzer tone (approx 100Hz)
Hmm. What else is here?
; If Track Switch No 8 held, skip the OS checks
Let’s try that. And indeed – no buzzer.
Which means:
- Cpu works
- Memory access logic works (at least the part for the EPROM’s).
- DUART 3 works (because that one has the buzzer on it).
Which means this thing is way more alive than I first thought!
Time for bed…..